1. Technical Field
The invention relates to a magnetically held track and to a carriage movable along the track which carries a work element for performing work on a work surface to which the track is magnetically adhered. More particulary, the invention relates to such a rail and carriage system in which the rail is formed of a high-strength plastic material, enabling it to bend to tighter radii and conform to the curvature of the work surface, and to a carriage having a resiliently mounted drive wheel enabling it to compensate for irregularities in the track teeth along which the carriage is driven by an internal motor.
2. Background Information
Magnetically held tracks having gear teeth formed thereon or attached thereto, have been used for numerous years for moving a carriage containing a work tool, such as a cutting or welding torch, for performing work on a workpiece on which the track is adhered.
Examples of some of these prior art rail and carriage systems are shown in U.S. Pat. Nos. 3,226,027, 3,656,364, 4,241,664, 4,456,228 and 4,570,542. These prior art rails are all formed of a metallic material, such as aluminum, enabling it to readily bend in order to conform to the curvature of a workpiece, such as a large diameter metal tank. The carriage usually contains a motor and a drive wheel having gear teeth driven by the motor, which teeth drivingly engage and mesh with gear teeth formed on the metal track. The track teeth are either formed integrally in the metal strip of the track or are formed as a separate component and mounted thereon.
However, several problems are present in such prior art tracks. The metal which forms the track becomes wrinkled after several uses and does not return to its original shape. Furthermore, the metal is affected by the vast differences in temperature to which it is exposed during use and storage. Even minor deformations in the track caused by use or the environment will affect the driving relationship with the carriage, often resulting in the carriage binding on the track as it attempts to move therealong by the driving engagement between the drive wheel of the carriage and the gear teeth on the track. Furthermore, these prior art metal tracks are relatively limited in the size of the radius to which they may be bent due to the thickness in the metal required to provide a sufficiently rigid track to retain the accuracy of the meshing engagement of the gear teeth mounted thereon and the drive wheel.
Another problem that exists with current carriages used for such tracks is that the drive wheel of the carriage is normally mounted in a fixed position on the carriage and rotated by an internal drive motor. Even slight irregularities in the teeth on the track, either caused by manufacturing tolerances, the collection of dirt and debris therein during use, and/or flexing of the track due to its bending and/or distortion caused by heat and cold, can affect the driving relationship between the gear teeth of the drive wheel of the carriage and the gear teeth of the track, resulting in binding of the carriage thereon.
Therefore, there is a need for an improved rail and carriage system which supports a workpiece on the carriage, which rail has increased flexibility and longer life, and which is unaffected by changes in temperature on the rail, and is unaffected by irregularities in the track teeth or the collection of debris therein.